Our goal is to further elucidate the anatomical and neurochemical basis of gonadotropin secretion. Luteinizing hormone releasing hormone (LHRH) producing neurons play the primary role in gonadotropin secretion. However, LHRH neurons do not contain steroid receptors and, therefore, they are not direct targets of gonadal hormones. The feed-back effects of these hormones on LHRH release are mainly mediated by estrogen-sensitive neurons and circuits which are connected to the LHRH neurons. Experiments outlined in this proposal will further determine the location of the cells of origin of these afferent systems, including catecholamine and GABAergic neurons, as well as their inter- and afferent connections with other neuropeptide Y (NPY)- and beta-endorphin (beta-END)-containing neurons, which are known to play important roles in the regulation of LHRH neurons. The delineation of these connections will extend our understanding of the central regulation of gonadotropin hormone release and elucidate why, in different endocrine stages, the same transmitters can exert opposite effects on gonadotropin release. Furthermore, they will help to elucidate pathomechanisms of endocrine disease-and age-related malfunctions of the ovarian cycle. "Classic" correlated light and electron microscopic techniques will be combined with state-of-the-art electron microscopic double immunostaining methods and antero-and retrograde tracer techniques. The proposed experiments will define: 1) What is the anatomical basis of the involvement of the estrogen- sensitive zona incerta in the regulation of LHRH release? 2) Which type(s) of catecholamine cells are involved in the beta-END- mediated control of LHRH release? 3) What are the locations and types of GABAergic systems involved in the direct and indirect control of gonadotropin release? 4) Which type(s) of NPY neurons are involved in the direct and indirect regulation of LHRH neurons? 5) What is the synaptological basis of interactions between beta-END and dopamine, and brain stem norepinephrine systems?